Electro-hydrodynamic wind energy systems and methods

ABSTRACT

Provided are electro-hydrodynamic (EHD) system for extracting energy from wind. Also provided are injectors for producing particles in an EHD system. Additionally, methods for producing particles in an EHD system is also provided. Further provided are displays comprising an EHD wind energy system. Also, an electro-hydrodynamic wind energy system integrated with a display is provided. A method of generating electricity is also provided. Additionally, a method of displaying a message is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/214,852, filed 29 Apr. 2009, U.S. Provisional Application No. 61/247,481, filed Sep. 30, 2009, and U.S. Provisional Application No. 61/303,302, filed Feb. 10, 2010, all of which are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

This invention relates to electro-hydrodynamic wind energy conversion systems.

BACKGROUND OF THE INVENTION

Electro-hydrodynamic (EHD) wind energy conversion is a system where blowing wind acts on a spray of electrically charged droplets. These charged droplets are separated from their counter-charged source by the wind's energy. This negatively charged side can be connected to a load to produce a working current. See, e.g., PCT Patent Publication WO 2009/094441, filed Jan. 22, 2009, and U.S. Provisional Patent Application No. 61/247,481, filed Sep. 30, 2009 for examples of EHD wind energy conversion systems. Various, nonlimiting embodiments of EHD systems are illustrated in FIGS. 1-4 of WO 2009/094441. As illustrated therein, an EHD system generally comprises an upstream charged collector, an injector that injects particles into the wind, where the particles have a charge opposite to the upstream collector, and, optionally, a downstream collector having the same charge as the particles.

In an EHD system, both a droplet production means and a droplet charging means will contribute to the ability to produce net power from a device. These also contribute individually and together to the consumption of energy in such a system which results in efficiency reductions and should be minimized.

Numerous means of producing droplets are known in the art, few of which incorporate low energy consumption as a design criterion. Similarly, numerous means of forming an electric field with the objective of providing a charge on a droplet are known, however, specific means of designing such an electrode to minimize losses in an EHD wind system have not been identified.

The amount of charge on such a droplet will dictate the magnitude of the electrical forces acting against the wind. The velocity of the wind will dictate the magnitude of the drag forces allowing the droplet to move away from the negative source. Thus, for a given wind speed, specific droplet sizes and charge densities will permit positive net energy to be generated.

Disclosed herein are modifications of EHD wind energy systems that provide improved efficiency and greater control of energy output, and provide alternative configurations for these systems.

SUMMARY OF THE INVENTION

In some embodiments, an electro-hydrodynamic (EHD) system for extracting energy from wind is provided. The system comprises an upstream collector biased at an electrical potential, the electrical potential inducing an electric field; and an injector for introducing a particle into the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particle. In these embodiments, the upstream collector is discontinuous.

In other embodiments, an EHD system for extracting energy from wind is provided. The system comprises an upstream collector biased at an electrical potential, the electrical potential inducing an electric field; an injector for introducing a particle into the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particle; and a downstream collector. In these embodiments, the downstream collector is not in a parallel plane to the upstream collector.

Also provided is another EHD system for extracting energy from wind. The system in these embodiments comprises an upwind upstream collector biased at an electrical potential, the electrical potential inducing an electric field; an upwind downstream collector positioned to collect particles from the upwind injector; a downwind upstream collector biased at an electrical potential, the electrical potential inducing an electric field; an upwind injector for introducing a particle into the electric field induced by the upwind upstream collector, wind drag on the particle being at least partially opposed by a force of the electric field on the particle; and a downwind injector for introducing a particle into the electric field induced by the downwind upstream collector, wind drag on the particle being at least partially opposed by a force of the electric field on the particle.

An additional EHD system for extracting energy from wind is further provided. The system comprises an upstream collector biased at an electrical potential, the electrical potential inducing an electric field; an injector for introducing a particle into the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particle; and a downstream collector. In this system, the distance between the injector and the downstream collector is adjustable.

Additionally provided is still another EHD system for extracting energy from wind. The system comprises an upstream collector biased at an electrical potential, the electrical potential inducing an electric field; and an injector for introducing a plurality of particles into the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particles. In this system, the plurality of particles comprise cesium.

Further provided is yet another EHD system for extracting energy from wind. The system comprises an upstream collector biased at an electrical potential, the electrical potential inducing an electric field; and an injector for introducing a plurality of particles into the electric field, wind drag on the particles being at least partially opposed by a force of the electric field on the particles. In this system, the plurality of particles carry an average charge less than about 75% of the Rayleigh limit.

Additionally, another EHD system for extracting energy from wind is provided. The system comprises an upstream collector biased at an electrical potential, the electrical potential inducing an electric field; and an injector for introducing a particle into the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particle. In this system the injector is the injector described immediately above.

Further provided is an injector for producing particles in an EHD system. The injector comprises at least one nozzle designed to emit fluid particles; and an electrode positioned adjacent to the at least one nozzle. In these embodiments, the electrode generates an electric field that is at a higher field concentration at a point closer to the at least one nozzle than to the electrode.

An additional EHD system for extracting energy from wind is provided. The system comprises an upstream collector biased at an electrical potential, the electrical potential inducing an electric field; and an injector for introducing a particle into the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particle. In these embodiments, the injector is the injector described immediately above.

A method for producing particles in an EHD system is also provided. The method comprises positioning a plurality of nozzles designed to emit fluid adjacent to an electrode; generating an electric field at the electrode such that the electric field generated by the electrode is at a higher field concentration at a point closer to the nozzle than to the electrode; and emitting the fluid under pressure through the nozzles to produce particles.

Additionally provided is a display comprising an electro-hydrodynamic wind energy system and visible graphics.

Also, an electro-hydrodynamic wind energy system integrated with a display is provided that further comprises visible graphics.

Further provided is a method of generating electricity. The method comprises obtaining the electro-hydrodynamic wind energy system described immediately above and operating the system to generate electricity.

A method of displaying a message is additionally provided. The method comprises obtaining the above-described display and operating the electro-hydrodynamic wind energy system to generate electricity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an upstream collector in accordance with an illustrative embodiment.

FIG. 2 is a perspective view of an upstream collector in accordance with an illustrative embodiment.

FIG. 3 is a diagram of injectors and a downstream collector in accordance with an illustrative embodiment.

FIG. 4 is a diagram of injectors and downstream collectors in accordance with an illustrative embodiment.

FIG. 5 is a diagram of an inkjet printer in accordance with an illustrative embodiment.

FIG. 6 is a graph of a square wave nozzle voltage in accordance with an illustrative embodiment.

FIG. 7 is a cross section of a nozzle and a filter element in accordance with an illustrative embodiment.

FIG. 8 is a perspective view of a modular element of louvers comprising injectors and upstream collectors in accordance with an illustrative embodiment.

FIG. 9 is a perspective view of modular elements of louvers comprising injectors and upstream collectors in accordance with an illustrative embodiment.

FIG. 10 is a perspective view of a nozzle in accordance with an illustrative embodiment.

FIG. 11 is a perspective view of a nozzle in accordance with an illustrative embodiment.

FIG. 12 is a perspective view of a nozzle in accordance with an illustrative embodiment.

FIG. 13 is a perspective view of a nozzle in accordance with an illustrative embodiment.

FIG. 14 is a perspective view of a nozzle in accordance with an illustrative embodiment.

FIG. 15 is a perspective view of a nozzle in accordance with an illustrative embodiment.

FIG. 16 is a perspective view of a ring shaped electrode positioned coaxially with a nozzle in accordance with an illustrative embodiment.

FIG. 17 is a perspective view of an array of ring shaped electrodes each positioned coaxially with a nozzle, in accordance with an illustrative embodiment.

FIG. 18 is a perspective view of a ring shaped electrode positioned circumferentially to a plurality of nozzles in accordance with an illustrative embodiment.

FIG. 19 is a perspective view of a plurality of linear electrodes positioned adjacent to a corresponding linear array of nozzles in accordance with an illustrative embodiment.

FIG. 20 is an expanded perspective view of the linear electrodes and linear arrays of nozzles of FIG. 19.

FIG. 21 is a perspective view of a display comprising a plurality of EHD systems in accordance with an illustrative embodiment.

FIG. 22 is a perspective view of a module of injectors and upstream collectors as used in the display of FIG. 21.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Additionally, the use of “or” is intended to include “and/or”, unless the context clearly indicates otherwise.

Provided herewith are modifications of electro-hydrodynamic (EHD) wind energy systems that provide improved efficiency and greater control of system components as well as provide alternative configurations for these systems. As elaborated in PCT Patent Publication WO 2009/094441, an EHD wind energy system requires the following:

-   -   The separation of positive from negative charge within an         otherwise neutral fluid;     -   The deposition of a charge on water droplet;     -   The separation of the charged water droplet from the opposite         charge by wind; and     -   The collection of the opposite charge to do work

Opposing charges are drawn towards one another. The force between opposing charges can be defined by an electrostatic field. As more droplets are driven away by the wind, ever more opposite charges are left behind, thus building up an ever-larger field. For a given wind speed and particle size, there is a field strength that will overcome the wind force, and particles can no longer be blown away. In some embodiments, systems are provided herein that control the maintenance of a steady-state balance whereby the wind force is always strong enough to separate charged droplets from their source, thereby enabling collection of charge left behind.

For a given wind speed, atmospheric pressure, temperature, and humidity, a given droplet will evaporate more or less quickly. In order to work, the droplet must make transit across a certain working distance before evaporating completely and releasing its charge into the atmosphere. In the space between nozzles and the downwind collector, the electric field may change considerably due to increased particle distance from the upwind collector as well as due to presence of other charged particles. In some positions, the electric field from other particles may add to field resistive force; in other positions it may subtract.

In the case where wind energy is high, and resulting particle charge densities must also be high, it is advantageous to construct the collector area to allow charge spreading due to internal space charge repulsion. In various embodiments, a collector is long and skinny, thus allowing charges to expand upward and downward. A example of such a collector is provided in FIG. 1. The upstream collector 10 comprises a support frame 14 and electrospray louvers 16 (further described in PCT Patent Publication WO 2009/094441). This collector releases a spreading electrospray plume 18. To take further advantage of the spreading electrospray plume, an upstream collector is provided herein that is discontinuous, i.e., the upstream collector is in more than one unit, spread apart, to allow charge spreading between the units. Thus, an EHD system for extracting energy from wind is provided. The system comprises an upstream collector biased at an electrical potential, the electrical potential inducing an electric field; and an injector for introducing a particle into the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particle. In these embodiments, the upstream collector is discontinuous. FIG. 2 provides a nonlimiting example of such an upstream collector. The illustrated upstream collector 20 is comprised of 9 modules 22. Each module 22 comprises a frame 24 and electrospray louvers 26. The electrospray plume 28 spreads into the spaces between the modules, which spreads out the space charge.

These EHD systems can be utilized in any EHD system known in the art, for example any EHD system described herein or in PCT Patent Publication WO 2009/094441. In some embodiments, the EHD system comprises a downstream collector.

An EHD system has considerable flexibility in the size and shape of the downstream collector, including systems that have no downwind collector at all. Given that the downstream collector shapes the working field and additionally helps direct the flow of ions passing from emitters downwind, it is advantageous to shape the downstream collector so that ion work extraction is maximized, while parasitic effects are minimized. Any downstream collector shape achieving that advantage for a particular upstream collector and injector design can be utilized, for example downstream collectors that are not in a plane that is parallel to the upstream collector. Thus, in various embodiments, an EHD system for extracting energy from wind is provided. The system comprises an upstream collector biased at an electrical potential, the electrical potential inducing an electric field; an injector for introducing a particle into the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particle; and a downstream collector. In these embodiments, the downstream collector is not in a parallel plane to the upstream collector. These configurations can be adapted to any EHD system known, for example, any EHD system described herein or in PCT Patent Publication WO 2009/094441. In some embodiments, the injectors are electrospray injectors.

The downstream collector can have any useful shape. A nonlimiting example is illustrated in FIG. 3, which shows an EHD system 30 comprising an array of injectors 32, an upstream collector 33, and a concave downstream collector 34.

In high winds the energy density is often high enough that an EHD WEC system cannot entrain enough charge to extract a reasonable percentage of energy. For such cases, a multiple stage EHD system is provided herewith. Such an EHD system comprises an upwind upstream collector biased at an electrical potential, the electrical potential inducing an electric field; an upwind downstream collector positioned to collect particles from the upwind injector; a downwind upstream collector biased at an electrical potential, the electrical potential inducing an electric field; an upwind injector for introducing a particle into the electric field induced by the upwind upstream collector, wind drag on the particle being at least partially opposed by a force of the electric field on the particle; and a downwind injector for introducing a particle into the electric field induced by the downwind upstream collector, wind drag on the particle being at least partially opposed by a force of the electric field on the particle. In some embodiments, the system further comprises a downwind downstream collector positioned to collect particles from the downwind injector. An example of such a multistage EHD system is illustrated in FIG. 4, showing the system 40 comprising upwind injectors 42, an upwind upstream collector 43, an upwind downstream collector 44 having a concave shape, downwind injectors 46, an upwind downstream collector 45, and a downwind downstream collector 48, also having a concave shape.

These systems can further comprise a third stage, which could be useful in areas having persistent high winds.

These EHD systems can be utilized in any EHD system known in the art, for example any EHD system described herein or in PCT Patent Publication WO 2009/094441.

An EHD system could become more efficient by reducing the space charge limit. Whealton, et al. (1999) have reported a reduction in the space charge limit in hydrogen negative ion sources by addition of cesium to the ion flow. Such a reduction in space charge limit by adding cesium to the particle stream would be useful for improving the efficiency of EHD systems because reduction in space charge limits results in generally higher system current flows.

Thus, additionally provided is still another EHD system for extracting energy from wind. The system comprises an upstream collector biased at an electrical potential, the electrical potential inducing an electric field; and an injector for introducing a plurality of particles into the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particles. In this system, the plurality of particles comprises cesium.

These EHD systems can be utilized in any EHD system known in the art, for example any EHD system described herein or in PCT Patent Publication WO 2009/094441. In some embodiments, the EHD system comprises a downstream collector. In other embodiments, the injector is an electrospray injector.

The maximum amount of charge that a fluid particle can hold is defined by the Rayleigh limit Q_(max). The Rayleigh limit is calculated using the formula

Q_(max)=8π√{square root over (σεR¹)}

Where:

Q_(max) is the maximum amount of charge in coulombs,

ε is the vacuum permittivity,

σ is the surface tension of the liquid, and

R is the radius of the droplet.

Droplets with charge at or near Q_(max) may subsequently exceed the maximum charge limit by evaporating, thus causing them to explode into smaller droplets. This phenomenon is known as coulombic explosion. In direct current (DC) electrospray, droplets on the order of 1/10 the producing needle diameter are ejected with high frequency and charge that can approach the Rayleigh limit. However, droplets with charge considerably below that limit has the advantage of being less subject to electric field forces and relatively more subject to wind drag forces. Thus, in situations with high energy and field density, less-charged droplets provide improved system energy output. The tradeoff for this approach is that more water must be used to carry a given amount of system current. Another advantage of less-charged droplets is that they are less inclined to experience coulombic explosion as a result of evaporation. These efficiencies can thus be realized by controlling droplet size and charge density based on environmental conditions.

Under high humidity, high atmospheric pressure, and fast wind, smaller droplets are advantageous because evaporation is suppressed and transit time across the field space is small. Under these conditions, the EHD system controller can be adjusted to create smaller droplets. Charge per droplet may be adjusted as well, for a given droplet size, so that the wind force is just strong enough to push it through the strongest part of the opposing fields.

Each charged droplet is analogous to a canoe being paddled up river, where the river current (electric field) is opposed by paddling work (wind drag). It is beneficial to be able to adjust the width of the canoe paddles to get more force, or slow down the river so that a given paddle size can make faster progress with respect to the shore. Likewise, it is beneficial to be able to adjust the balance of forces surrounding a droplet. Efficiency in an EHD system can thus be gained by adjusting all key droplet parameters: droplet size, droplet charge, and electric field strength. In the majority of wind conditions, the droplet is preferably charged at significantly less than the Rayleigh limit, depending on the mix of droplet size, field strength, wind speed, and atmospheric conditions.

Thus, another EHD system for extracting energy from wind is provided. The system comprises an upstream collector biased at an electrical potential, the electrical potential inducing an electric field; and an injector for introducing a plurality of particles into the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particles. In this system, the plurality of particles carry an average charge less than about 25% of the Rayleigh limit. In some of these embodiments, the plurality of particles carry an average charge less than about 20% of the Rayleigh limit. In other of these embodiments, the plurality of particles carry an average charge less than about 15%, 10%, 5%, or 1% of the Rayleigh limit. The Rayleigh limit is calculated by measuring the current (generally measured in Coulombs/sec), flow rate (m³/sec), and average droplet size (m³) to derive Coulombs/m³, which directly relates to Rayleigh charge percentage.

These EHD systems can be utilized in any EHD system known in the art, for example any EHD system described herein or in PCT Patent Publication WO 2009/094441. In some embodiments, the EHD system comprises a downstream collector. In other embodiments, the injector is an electrospray injector.

While electrospray, with variants on the Taylor cone modes, is a key means of producing charged droplets, there are other applicable methods. Ink jet printers have been reliably producing charged droplets for decades. While the energy consumption of most ink jet processes does not match EHD's nozzle requirements, the continuous ink jet, or CIJ does. A typical CIJ nozzle puts out droplets continuously, as the name states, rather than on-demand. A CIJ nozzle works by forcing fluid through a nozzle, and simultaneously vibrating the exiting fluid column with a suitable wavelength. At the right frequency, the exiting fluid column pinches off droplets at lengths corresponding to wave function nodes. FIG. 5 is a diagram of a CIJ system, showing a vibrator waveform 50, fluid reservoir 51, nozzle 52, fluid column 53, charged droplets 54, piezoelectric vibrator 55, wavelength 56, and charging electrode 57. A CIJ system as shown can be used as an injector with any EHD system known in the art, for example any EHD system described herein or in PCT Patent Publication WO 2009/094441.

Droplet size control is critical because the droplet diameter creates the cross section upon which wind drag may act. Wind drag control is required in order for EHD to work properly, and that means droplet size control is critical. It is comparable to being able to control the blade pitch angle and rotational speed of a conventional wind energy conversion turbine.

For a given nozzle size, the electric field that creates the droplet, the flow rate of fluid, and the pressure into the nozzle can be controlled, as well as the time-varying shape of the forming electric field. In the simplest case, for a given flow rate, the field is simply DC. In other cases, the field is a sinusoidal AC signal, an AC signal with specific repeating wave forms, a square wave, with variable average, minimum-maximum, pulse width, or frequency. The AC square wave may also have steps within a repeating form, or a square wave function could be with an analog function, such as a square wave form front pulse followed by an analog tail with specific form. Additionally, the nozzle or the column of fluid exiting the nozzle can be vibrated in order to influence the position along the exiting column where fluid droplets are pinched off.

FIG. 6 depicts a square wave nozzle voltage, referenced to the field electrode. It has a frequency of 100 kHz, an average voltage of 4 kV, a peak voltage of 4.5 kV, and amplitude of 3.5 kV. Further discussion of the effect of AC fields of varying frequencies may be found in Maheshwari and Chang (2006).

A combination of pressure, flow, AC, DC, pulsing, waveform shape, and fluid column vibration also alters the charge per droplet. A droplet at the point of release or formation may not be fully charged because it leaves the charging region before mobile ions have a chance to fully enter or exit the droplet. For instance, the deformation energy added to a Taylor cone by a square wave pulse may add enough momentum to the tip to overcome surface energy. If this is coordinated with a depleted rate of ion flow, then a droplet of chosen size and charge may be formed.

It is also typically advantageous to create droplets that are uniform in size, or monodisperse. In other instances, a varied droplet size is adequate. For instance, in very high winds, nearly all droplet sizes are suitable for traversing the working field. In such a case, it is useful to increase the nozzle flows and voltages to maximum. In such a condition, the nozzles will produce a variety of particle sizes with varying charge.

Nozzle clogging must be avoided for continued operation. While incoming fluid will be processed and filtered, there are always internal sources of particles. Such internal sources include corrosion, mechanical attrition, agglomeration of smaller particles, or precipitation of dissolved solids. In-situ filtration is a means of providing point-of-use fluid conditioning by place a small filter element just upstream of the nozzle inlet. Where there are multiple, adjacent nozzles, this filter may also act as a distributor by causing pressure loss into the final feed chamber along the length of the distributor head. FIG. 7 shows a cross section of such an element 70, deposed in a straight section of the airfoil 72, showing a nozzle 74 deposed at the leading edge of the airfoil 72. The advantages of airfoils in controlling wind dynamics is discussed in PCT Patent Publication WO 2009/094441

The inherently modular nature of EHD WEC makes it well suited for portable applications. Two pivotal design considerations for portability are 1) light weight, and 2) small size. As long as modular elements are movable by one or two persons, a system can be unitized, moved, and set up.

A typical modular element for a portable system would be a unit area element. For example, the area element might be a 1×4 meter area designed to produce 1 kW in a 25 mph wind. FIG. 8 shows such an element 80. Four rigid tubes 82 define the outside of the collection area, comprised of an array of louvers 84 internally. The louvers 84 consist of alternating rows of airfoil. Every other airfoil is an electrospray nozzle element; in between the nozzle elements are the field electrode elements.

Another approach to modular, portable construction is to make complete repeating units that are light and small. These units contain all louver elements and the surrounding frame. Units are clipped together to form whatever sized collection area is desired. FIG. 9 illustrates an example of such a construction. The figure omits consideration of electrical, hydraulic, and pneumatic hook-ups for simplicity. A complete system also includes power conditioning, water storage or sourcing, water conditioning, controls, and various connections. In FIG. 9, an external frame 92 encompasses louvers 94, which consist of alternating rows of airfoil, where every other airfoil is an electrospray nozzle element; in between the nozzle elements are the field electrode elements.

To minimize weight, the external frame and louver assembly are stabilized by external tensile elements such as wire struts. In some embodiments, the entire assembly is mounted to a gimbal that permits positioning of the collector area normal to the wind.

The mounting gimbal may be attached to the ground, or it may be perched on top of a tower in order to give the system more height. Portable applications can also use a telescoping tower to attain good heights during operation, but requiring minimal storage lengths.

Completing the portable EHD system are additional elements such as water storage and conditioning, water pumping, and power conditioning. These systems must be designed to be light weight as well.

EHD wind energy systems can use a variety of fluid sources, and may entrain fluids with certain properties. Potential fluid sources include fresh, brackish, or seawater, well water, rain water, or water extracted by condensation from the atmosphere. Water is optionally passed through an ion exchange bed in order to provide the right concentration of preferred ions. It is preferably also passed through a filter that assures clean passage through the nozzles.

It can be beneficial to add surfactant to the water in order to lower its surface tension. Lower surface tension makes formation of droplets less energy intensive. Additionally, native fluid may have electrical conductivity that is too high or low, and needs to be adjusted accordingly. Any additions to the working fluid must certainly be compatible with the environment. Certain additives may be beneficial to the environment, such as a surfactant that serves its EHD purpose, and then falls to the earth as fertilizer.

Where tower heights are high or water sources are generally low with respect to the EHD nozzles, energy to pump the fluid to height must be considered against the energy needed to condense system water from the atmosphere.

Since evaporation is a serious consideration for droplet lifetime and system performance, it is beneficial in some circumstances to create droplets that form a surface coating that inhibits evaporation. Dual outlet electrospray nozzles known in the art can coat water droplets with oil. Alternatively, water additives are available that form an inhibiting outer layer once a droplet has experienced some initial evaporation. Additionally, common salts or other dissolved solids inhibit evaporation by increasing their concentration as a droplet loses water content. These elements may also be employed as evaporation inhibitors. Preferably, they are environmentally benign such that they do not result in harmful buildup of materials downwind from collectors.

Nozzles for producing charged droplets can take any of a variety of forms, for example blunt (for example as illustrated in FIG. 10), tapered (for example FIG. 11), double-ground (for example FIG. 12), sharp tip in nozzle (for example FIG. 13), and laser cut (for example FIG. 14).

A blunt tip (FIG. 10) is simplest, and can be created by individually mounting individual nozzles. A laser cut hole and boss (FIG. 14) mimics the straight nozzle, and has the advantage of being mass produced along a line or in a pattern from a single piece during a continuous fabrication process.

A double ground tip (FIG. 12) has two edged surfaces that enhance field strength because of their sharp points. Placing a sharp tip inside a fluid source like a nozzle (FIG. 13) permits a strong field to be formed at the solid tip. Fluid is drawn to the tip by capillary action, and emitted as droplets from the tip.

An open form nozzle, similar in concept to the sharp tip nozzle, is one that has an active edge, optionally serrated, with open feed slots for example as illustrated in FIG. 15. Fluid is fed through the slots, or through an equivalent series of orifices. The fluid is drawn to the active edge, whose geometry enhances the field in a manner similar to that of the single needle tip. Fluid is ejected from the edge at discrete points. The edge may be serrated to provide further field enhancement.

A nozzle can be made of any material that provides the right fluid path, channel diameter, and nozzle height above datum. Common materials for nozzle fabrication are metal, typically stainless steel, and plastic.

Nozzles may be formed or inserted in a plastic extrusion process. Alternatively, a roll-formed airfoil may have nozzles created or inserted, and a plastic filter element inserted afterward.

The outer frame must be stiff in order to withstand wind forces. With proper anchoring, the frame can be light for portability. It must also be multi-functional in that some portions of the frame may optionally contain hydraulic, pneumatic, and electrical elements required to support and control the electrospray process.

Further provided is another injector for producing particles in an EHD system. The injector comprises at least one nozzle designed to emit fluid particles; and an electrode positioned adjacent to the at least one nozzle. In these embodiments, the electrode generates an electric field that is at a higher field concentration at a point closer to the at least one nozzle than to the electrode. In additional embodiments, the nozzle and electrode serve as the upstream collector.

One embodiment of these injectors is shown in FIG. 16. The injector 160 provides a horizontally oriented nozzle 162 (i.e., one in which the spray orifice emits droplets in the same direction as the wind), in combination with a ring electrode 164 for field spreading. The ring electrode 164, made of conductive material, is placed with its ring axis concentric with the axis of the needle or nozzle 166, with its planar position variable fore, co-planar, or aft of the tip of the needle 166. The ring electrode 164 maintains high field concentration at a spray orifice tip 168 with rapid drop-off of field [volts/meter] heading radially outwards towards the ring electrode 164, thus facilitating high field strengths for electrospray, or atomization methods, but not providing a current path for short circuiting. The field drops off sufficiently near the ring electrode 164 to prevent corona discharge (shorting), even with high fields near the needle 166 or other spray device.

Use of a large diameter (⅛-¼ inch) cross-section wire or rod to form the ring electrode 164 improves the shape of the electric field lines such that charging occurs, but short circuiting is reduced. A large diameter ring electrode provides a large space between a needle or nozzle or other spray device and the field electrode, creating a large sweeping area for wind to carry charged species away. Entrainment of charged particles is enhanced significantly, while reducing short circuiting.

FIG. 17 shows multiple needles 166, nozzles 162 and ring electrodes 164 structured as an array. Alternatively, as shown in FIG. 18, multiple needles 166 or spray devices can be placed within a single ring electrode 164 to admit multiple sprays being charged by a single ring shaped field electrode 164.

Ring electrodes as described have numerous attractive features but are limited in the number of spray devices they can service. As shown in FIG. 19, a linear electrode 190 that produces a horizontal field spreading can have advantages similar to those of a ring electrode, but provides additionally for long arrays of needles or nozzles 192 or other spray devices, and more efficient use of collector area (rectangles vs. circles). An expanded view of the linear electrodes 190 and nozzle arrays 192 are illustrated in FIG. 20.

In some embodiments, the field electrode has an airfoil cross section. Such an electrode has more favorable drag characteristics than an electrode with a circular cross section, which can produce turbulence in the air flowing over it. This provides benefits such as minimizing air flow resistance, retaining and supporting laminar rather than turbulent flow, and increasing the efficiency of charged droplet or particle entrainment in the wind stream such that short circuiting and inefficiency are minimized.

DC electrospray atomization as a means of creating charged droplets for EHD wind energy is discussed in PCT Patent Application WO 2009/094441. However, limitations on the size and charge density of droplets that can be produced using DC electrospray may limit its utility in EHD wind applications. Specifically DC electrospray produces very small droplets (<5 microns) with a high charge density (60% or more of the Rayleigh limit) which may result in space charge limited operation and sub-optimal output. AC electrospray, in which the amplitude of the voltage and its polarity in an electrospray system is varied at user selected frequency can provide increased control over both the droplet sizes produced and the charge density on the droplets. Even a neutral charge can be achieved by these means. So, larger droplets with lower charges which are more favorable in terms of net potential output can be obtained.

Conventional electrospray atomization relies exclusively on the use of an electric field to promote the formation of droplets using a meniscus formed at the end of a needle or a nozzle. Very low pressures, of less than 1 psi, or even modestly negative pressures are employed, and the presence of a high charge density causes a droplet to form and detach itself as a critical charge density which exceeds the Rayleigh limit accumulates at the very small tip of an elongated meniscus. In contrast, standard pressure nozzles rely on various mechanical design features in combination with hydraulic pressure to produce a spray of droplets.

Because EHD wind energy conversion is optimized by producing a droplet in the size range readily achievable by conventional nozzle atomization and with a reduced charge density, a field electrode may be combined with a spray nozzle incorporating one or more features designed to promote and control droplet formation. The result will be a reduced pressure required for atomization and the production of a charged droplet with subcritical charge density.

Some nozzle design features which may be useful include (but are not limited to):

Hollow cone shaped spray nozzle design, driven solely by hydraulic fluid action, incorporating a set of “swirl” features which impart a rotational component to the spray as well as the typical axial flow, the combination of which creates a ligament-based atomization mechanism, e.g., a swirl chamber;

A hollow cone spray design in which the spray is deflected by impacting a plate immediately post orifice exit, wherein said plate spreads the flow radially, e.g., a deflected type cone;

A hollow cone spray design wherein the exiting fluid column intersects an inward tapered spiral of material that peels off flow radially until there is nothing left, e.g., a spiral type cone;

A full-cone spray design whereby the fluid typically exits a nozzle orifice and encounters a bell-shaped exit region that draws fluid flow outward radially;

A full cone design that mimics the hollow cone design except that some fluid is allowed to traverse the entire peeling spiral axially and exit straight through, e.g., spiral type full;

A flat spray pattern design that takes its characteristic shape from the exit orifice, which is itself tapered at its two edges to resemble an eye, e.g., tapered flat;

A flat spray with a slotted exit orifice whose shape is more open at the ends rather than tapered, e.g., even flat;

An efficient flat spray nozzle type that wherein a solid, straight fluid column immediately intersects a sloped and spreading deflection plate that broadens the fluid flow in to a fan, e.g., deflected flat;

An air atomizing nozzle that shoots a high velocity stream onto an atomizing plate internal to the nozzle, and utilizes a sweeping, mixing, breakup flow of air to entrain and distribute fine droplets;

An air atomizing nozzle that produces coaxial streams of fluid (central stream) and high-speed air (annular) whereby the fluid breakup is facilitated by; a) fluid velocity, and b) air-fluid mixing, causing ejection of fine droplets.

Nozzle designs of all of these types can be further rendered more efficient by incorporating certain features at their tips which serve to concentrate the electric field at the exit orifice, increasing the charge density on the fluid locally. Such features include but are not limited to narrow lands at the nozzle tip which inhibit droplet spreading, conical, tapered, rather than flat nozzle tips, and related features which promote electric field enhancement.

A further approach to focusing the electric field is a nozzle design in which an internal focusing electrode is incorporated along the central axis. The end of the electrode is made pointed, to focus the electric field locally, and the tip is positioned in the fluid stream just prior to or nearly coincident with the nozzle exit. In optional combination with a tapered exterior nozzle surface, the externally applied electric field will concentrate in a region generally coincident with exiting fluid flow. Said concentrated field will preferentially select one charged species over another, causing entrainment in the exiting fluid stream and subsequent like charging of sprayed droplets.

Exiting fluid can itself be purposely shaped to promote field enhancement, mimicking Taylor cone type geometry field enhancement. The focusing geometry of the fluid may be as simple as a necking down of the fluid flow, similar to a vena contracta, or an exit orifice tapered inward to force a necking down, or the natural thinning and pointing of the edges of the fluid exit cone of a swirl nozzle. Field enhancement, as before, promotes migration of charged species to the charging tip or edge, and thus facilitates charging of the imminently ejected droplets.

Models of EHD wind energy systems show that both droplet diameter and droplet charge density affect the output of a system, along with wind speed. In general a smaller droplet size will produce a high output, until the droplet diameter becomes small enough to be less than the mean free path between gas molecules in the airstream. At this point, its drag cross section becomes so small that interaction with wind is insufficient, thus reducing its capability to extract the wind's kinetic energy. However, smaller droplets require more surface area to be created requiring additional pumping energy. Similarly, lower charge density will generally increase the output of an EHD wind system, indicating that very small droplets with very low charge can produce the greatest gross output. However lower charge density requires more water to pumped, and even more surface to be created, and may result in reduced net energy output exclusive of pumping and hydraulic atomization energy used. Thus, for any given wind speed there is a unique droplet size and charge density at which the maximum net energy can be obtained, when the charge density and droplet size are simultaneously optimized for those conditions.

Since increases in the efficiency of an EHD wind energy system can be achieved by minimizing fluid pumping energy, it is also useful to consider means by which pumping energy can be drawn from the environment, increasing net operating efficiency. Examples include but are not limited to use of wind and wave energy to create pumping energy, or tapping natural head pressure from artesian sources, or suitably sloped streams. Wind turbines designed to pump water pre-date electricity generation by turbines by many decades. This approach can usefully be integrated with an EHD system to harvest the modest amount of pumping energy required. Thus, small turbines that convert wind energy directly to mechanical motion for pump or compressor work will be more efficient than converting that mechanical work to electricity and powering an electric pump or compressor.

EHD wind energy is anticipated to be uniquely well suited to off-shore implementation. Since moderate pressures are required, a pump that converts wave energy to pump or compressor energy to supply and distribute working fluid at EHD wind system working pressures (typically less than 20 psi) reduces the complexity or the overall system while increasing its efficiency. Conveniently, wave energy available for pumping varies with wind speed, and matches the required volumes of water.

EHD wind energy conversion systems, by virtue of their stationary nature, must be placed high atop a pole or tower to harvest meaningful amounts of energy. It would be desirable to utilize the high platform provided by the EHD systems for another purpose. The present invention provides an additional use for EHD systems, by combining the EHD system with a graphic display, so that the EHD system also serves as an advertising or branding vehicle.

Provided herein is an additional use for EHD wind energy systems. As shown in FIG. 21, the EHD system of FIG. 22 is integrated with a display to provide an advertising or informational function with the energy generating function of the EHD system. Thus, in some embodiments, a display comprising an EHD wind energy system and visible graphics is provided.

FIG. 21 shows one embodiment of the display, comprising a plurality of EHD systems 210. An individual system is shown in FIG. 22, where the system comprises a series of injectors 220 and upstream collectors 222, as described in detail in PCT Patent Publication WO 2009/094441.

Any EHD system known in the art can be utilized with graphics for the display, for example as described in WO 2009/094441. In some embodiments, the EHD wind energy system comprises the components of an upstream collector biased at an electric potential, the electric potential inducing an electric field; and an injector for introducing a particle into the electric field, where the particle can comprise one or more water droplets, wind drag on the particle being at least partially opposed by a force of the electric field on the particle. The EHD system can further comprise a controller for changing a parameter of the system in response to a change in an atmospheric condition. This controller is often coupled with a sensor for monitoring the ambient atmospheric condition. Nonlimiting examples of atmospheric conditions that can usefully be monitored by the sensor include ambient wind speed or direction, temperature, pressure, and humidity. The effect of changes in those atmospheric conditions on the EHD system can be compensated by adjusting parameters such as particle size, electric charge per particle, particle flow rate, electric potential, electric field strength, and a separation between the upstream collector and electrical ground. An atmospheric condition of particular importance for these EHD wind energy systems is wind direction. Control of the position of the system in relation to the wind direction is important for optimization of energy conversion capabilities. Movement of the system can help ensure proper wind orientation.

In various embodiments, the electro-hydrodynamic wind energy system comprises the components of a downstream collector biased at an electric potential, the electric potential inducing an electric field; and an injector for introducing a particle into an air stream that moves the particle through the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particle. Such systems are described in WO 2009/094441.

The energy required to effect the change in the parameter of the system, for example the orientation of the components of the EHD system, can be supplied from an external source, or from the electricity generated by the EHD system itself. In some embodiments, the electricity is supplied by the EHD system if sufficient electricity is available from the system, where an external electrical source, for example a battery or an AC or DC power source or supply, is provided if insufficient electricity is available from the EHD system.

In some embodiments, when components of the EHD system are moved to be properly oriented to the direction of the wind, the entire display is moved. In other embodiments, only a portion of the display, e.g., the EHD components that need to be properly oriented, are moved.

The display can comprise any graphics desired, including text and/or a design. The graphics can comprise, e.g., a commercial logo, for example when the display is a billboard or a company sign. In various embodiments, the shape of the entire display is distinctive for the logo being displayed. In other embodiments, the graphics comprise non-commercial informational text, for example road or address information when the display is used as a road sign.

The graphics may be provided in any form or on any portion of the display. For example, at least a portion of the graphics can be applied to a component of the wind energy system. Alternatively, the graphics can be applied to a portion of the display that is not a component of the wind energy system. This can be a structural portion of the display, or on a nonstructural portion that is provided for the sole purpose of displaying the graphics. In some embodiments, particularly where the graphics could be deposed between the wind and the EHD components, the graphics is applied to a material that allows wind to pass through, so as to provide minimal interference with the ability of the EHD to generate electricity. Examples of such material is a fabric (e.g., an open weave or porous fabric), a pierced plastic, a netting or a rigid frame. In alternative embodiments, the graphics are displayed on the downwind side of the EHD system, for example on a downstream collector.

The graphics can be made by any method known in the art. For example, the graphics can be printed, painted, silk screened, etched, laminated, and/or formed from light reflective material. In some embodiments, graphics is created by anodizing a surface of at least a portion of a component of the EHD system, for example the upstream collector.

In some embodiments, the various structures of the EHD system can be modified to be part of the graphic display. For example, the diffuser illustrated in FIG. 5 of WO 2009/094441 can, instead of having a conical shape, can take a shape having a square, rectangular or oval cross-section; other components of the EHD system that can be modified to be incorporated into the graphic display include the downstream or upstream collector, the injector, or the tubing used upwind to distribute droplets.

In various embodiments, the graphics comprises at least one light, either deposed on the display, or deposed away from the display to shine light on the display. There can be any number of lights utilized herewith. Any light source can be used in these embodiments, for example an incandescent light, a light emitting diode (LED), or a laser light. The light for these embodiments can be generated using electricity generated by the EHD system or from an external source. In some embodiments, the electricity for the lights is supplied by the EHD system if sufficient electricity is available from the system, where an external electrical source, for example a battery or an AC or DC power source or supply, is provided if insufficient electricity is available from the EHD system.

The light may be used to illuminate graphics deposed on the display, for example graphics painted therein. Alternatively, the lights can be deposed on the display to create the graphics.

In other embodiments, the graphics are created on the display by shining a light, e.g., a laser light, onto the display. For example, a laser light may be controlled to project onto the back of the sign shown in FIG. 21 to generate a logo or message.

In another embodiment, a light or series of lights may be disposed on a rotating blade, for example a blade of a wind turbine. For example, linear arrays of light can be deposed along blades of a turbine, wherein each light can be turned on or off on the turbine at particular times to create a highly visible, sweeping array of text, images, or combined media. Such light controls are known in the art.

Also provided herewith is an EHD wind energy system integrated with a display further comprising visible graphics. As with the above-described embodiments, the graphics of this embodiment comprises text and/or a design, including a commercial logo or non-commercial informational text. In some embodiments, at least a portion of the graphics is applied to a component of the wind energy system. In other embodiments, the graphics is applied to a portion of the display that is not a component of the wind energy system.

Also as with the above-described display, the graphics of these embodiments can be made by any method known in the art. For example, the graphics can be printed, painted, silk screened, etched, laminated, and/or formed from light reflective material. In some embodiments, graphics is created by anodizing a surface of at least a portion of a component of the EHD system, for example the upstream collector. Alternatively or additionally, the graphics can comprise at least one light, e.g., an LED or laser. The light in these embodiments may be generated using electricity generated by the system, or an external source, or both, as described above.

In some embodiments, the EHD wind energy system here comprises components including an upstream collector biased at an electric potential, the electric potential inducing an electric field; an injector for introducing a particle into the electric field, wind drag on the particle being at least partially opposed by a force of the electric field on the particle; and a controller for changing a parameter of the system in response to a change in the atmospheric condition. The system can additionally comprise a sensor for monitoring an ambient atmospheric condition, for example ambient wind speed or direction, temperature, pressure, and/or humidity. Further, the electricity to change a parameter as needed (as determined by the sensor) may be effected using electricity generated by the system, from an external source, or both, as described above. Examples of parameters that can be changed are particle size, electric charge per particle, particle flow rate, electric potential, electric field strength, and a separation between the upstream collector and electrical ground, as described above.

Also provided herein is a method of generating electricity. The method comprises obtaining the above-described system and operating the system to generate electricity.

Further provided is a method of displaying a message. The method comprises obtaining the above-described display and operating the EHD wind energy system to generate electricity.

The system may also include a source of water and a pump for pressurizing the water for injecting water particles into the air stream.

Other embodiments within the scope of the claims herein will be apparent to one skilled in the art from consideration of the specification or practice of the invention as disclosed herein. It is intended that the specification be considered exemplary only, with the scope and spirit of the invention being indicated by the claims.

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In view of the above, it will be seen that the several advantages of the invention are achieved and other advantages attained.

As various changes could be made in the above methods and compositions without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

All references cited in this specification are hereby incorporated by reference. The discussion of the references herein is intended merely to summarize the assertions made by the authors and no admission is made that any reference constitutes prior art. Applicants reserve the right to challenge the accuracy and pertinence of the cited references. 

1-99. (canceled)
 100. An injector for producing charged particles for an electro-hydrodynamic system that extracts energy from a gas stream, the injector comprising: a hydraulic spray nozzle that injects a liquid droplet into the gas stream from a nozzle tip; an electrode, adjacent the nozzle, that generates an electric field with a higher field concentration at a point closer to the nozzle than to the electrode, wherein the electrode charges the liquid droplet; wherein the drag of the gas stream on the liquid droplet at least partially opposes the drag of the electric field on the droplet.
 101. The injector of claim 100, wherein the nozzle employs rotational motion to create the droplets.
 102. The injector of claim 101, wherein the nozzle further employs translational motion to create the droplets.
 103. The injector of claim 102, wherein the nozzle forms a hollow cone spray pattern.
 104. The injector of claim 103, wherein the nozzle includes a swirl nozzle.
 105. The injector of claim 100, wherein the nozzle tip concentrates the electric field.
 106. The injector of claim 105, wherein the nozzle tip is tapered.
 107. The injector of claim 100, wherein the injector further includes an internal electrode within the nozzle.
 108. The injector of claim 107, wherein the internal electrode is incorporated along the central axis of the nozzle.
 109. The injector of claim 100, wherein the internal electrode includes a pointed tip, wherein the electrode tip is substantially coincident with the nozzle tip.
 110. The injector of claim 100, wherein the droplet carries a charge less than approximately 25% of the Rayleigh limit.
 111. The injector of claim 100, wherein the electrode is a linear electrode.
 112. The injector of claim 111, wherein the electrode is disposed downstream of the nozzle exit.
 113. The injector of claim 100, wherein the nozzle further includes a filter upstream of the nozzle tip.
 114. An electro-hydrodynamic system that extracts energy from a gas stream, the system comprising: an injector that injects a plurality of particles of a single polarity into the gas stream, the injector including: a hydraulic spray nozzle that emits the particles from a nozzle exit; an electrode, adjacent the nozzle, that generates an electric field with a higher field concentration at a point closer to the nozzle than to the electrode, wherein the electrode charges the particle; wherein the drag of the gas stream on the particle at least partially opposes the drag of the electric field on the particle, and wherein the injector collects particles of the opposite polarity to the injected particle; a downstream collector, disposed downstream within the gas stream, that collets the injected particles; and a load, electrically coupled between the injector and the downstream collector.
 115. The system of claim 114, wherein the nozzle is a swirl nozzle including a swirl chamber and the particles are liquid droplets atomized from a liquid stream, wherein the swirl nozzle utilizes a rotational force to shear the liquid droplets from the liquid stream. 